The Dragonfires in the Temple of the One go out upon the death of each Emperor, and must be lit anew by each new Emperor (who must be a Dragonborn) upon their coronation. Akatosh created the Dragonfires with a burning handful of his heart's blood. The Dragonfires themselves are the ward against the planes of Oblivion; though it has been suggested several times in the Main Quest that it protects against all immortal realms. While they are lit, Daedra cannot exist permanently in Tamriel and portals to Oblivion are not possible.